Mobile telephones for use in radiotelephone networks (“cellular telephones”) are in widespread use, and cellular telephone calling plans define how much a user is charged for the use of a cellular telephone. The billing rules of cellular telephone calling plans can be complex. For example, a typical calling plan provides for a fixed number of minutes over a given period of time, such as a month, for a flat fee. In addition, the calling plan typically provides that calls must be made from or received within a specific geographic area or areas (“calling area”). Additional charges may be assessed for minutes in excess of the fixed number of minutes, for calls from outside of the calling area (“roaming calls”), for calls to numbers outside of the calling area (“long distance calls”), and for calls made on particular days of the year or week, or at a particular time of day. In addition, a calling plan may count the time required to make a connection as part of the call's duration and may round up the duration of the call to a whole number of minutes. Further, some calling plans do not count the first minute of a call when computing call duration. Other plans provide different rules depending on whether a call is incoming or outgoing. Moreover, some plans permit allocated minutes to be carried over from one billing period to the next. In addition, some calling plans cover the use of two or more telephones under a single plan (“shared minutes”). A calling plan may have many combinations and permutations of a large number of the limitations and conditions mentioned above.
A user may wish to accurately track these charges and thereby budget his use of the cellular telephone. Some cellular telephones include a cumulative call timer that keeps a continuous record of phone use since the last time the timer was reset. However, for the purpose of budgeting cellular telephone expenses, the cumulative call timer has significant limitations. Because there may be no charge for the first minute of a call, the cumulative call timer may start accruing time too early. On the other hand, because the time period of the call may include the time required for a connection to be established, the cumulative call timer may start accruing time too late. The cumulative call timer may not easily be used to estimate the cost of a call because the rate of charge applied to the particular call may depend on the sum of the duration of all similar calls previously made in the billing period, that is, whether the fixed number of minutes in the calling plan have been exceeded. In addition, the cumulative call timer does not account for the caller's location or the number called and, as mentioned above, these factors may affect the charge rate. Further, in order to estimate the number of minutes used during a billing period, the cumulative call timer must be reset at the start of each new billing cycle. This requires the user to remember this date and manually reset the call timer. This is inconvenient and not commonly performed. In addition, a calling plan may provide for unused minutes to be carried over into the next billing period and the cumulative call timer cannot carry over minutes. For these reasons, the cumulative call timer generally does not provide a means for accurately estimating cellular telephone usage charges. Thus, it is often not practical, and in some cases not possible, for a cellular telephone user to track these charges and thereby budget use of the cellular telephone.
Accordingly, there is a need for a cellular telephone that provides automatic tracking of cellular carrier charges so that a user of the cellular telephone may budget the use of the cellular telephone and thereby lower the user's costs.